Improving Immunotherapy Responses by Dual Inhibition of Macrophage Migration Inhibitory Factor and PD-1

Macrophage migration inhibitory factor (MIF) is an upstream regulatory cytokine that is associated with advanced disease and poor outcomes in multiple cancer types, including melanoma. We investigated whether anti-MIF therapy could enhance the antitumor effects of the immune checkpoint inhibitor anti-PD-1 in two murine tumor models. The therapeutic efficacy of anti-MIF, alone or combined with anti-PD-1, was tested in the YUMMER1.7 melanoma and MC38 colorectal cancer models. Tumor growth and survival were assessed in untreated Mif knockout (KO) and low-expression human MIF allele (CATT5) mice and compared to wild-type (WT) or high-expression MIF allele (CATT7) mice. Tumor-bearing animals underwent cytokine profiling, tumor immunohistochemistry, flow cytometry, and single-cell RNA sequencing (scRNA-seq). We also correlated functional variant MIF alleles with melanoma incidence and progression in patients. Our results showed that combined anti-MIF and anti-PD-1 significantly reduced tumor growth, improved survival, and promoted tumor regression, accompanied by enhanced TH1 cytokine levels, macrophage activation, and increased type 1 conventional dendritic cells (cDCs). scRNA-seq analysis revealed an expansion of intra-tumor Cd74/C1q/Aif1-expressing macrophages, which exhibited an antitumor phenotype, in response to anti-MIF therapy. MIF-KO and CATT5 mice exhibited reduced tumor burdens compared to WT or CATT7 mice alone and in the presence of anti-PD-1. In melanoma patients, the high MIF expression genotype (-173C/C) occurred at higher frequencies compared to healthy controls. These findings highlight that the addition of anti-MIF to anti-PD-1 reduces tumor growth, enhances anti-tumor responses, prolongs survival, and augments key intratumor immune cell populations involved in immune activation against tumors. This approach merits further consideration for clinical trial development.